High-sensitivity imaging systems are often employed in computer vision systems to detect subtle differences in image features, particularly under low-light conditions. Such imaging systems are typically desirable when used with active illumination, such as structured light (e.g., a known light pattern of bars, grids, or the like), unstructured light, modulated light for time-of-flight (TOF) systems, and so forth. To accomplish this sensitivity, the lens aperture for the imaging system is typically increased, which limits the depth of field (DOF) of the imaging system at many lens positions.
In such systems, a variable focus actuator that moves the lens along its optical axis, closer to or further away from the aperture, is often employed to expand the overall working range of the imaging system. However, in many computer vision applications, the intrinsic characteristics of the imaging system change as the position of the lens changes. Examples of these intrinsic characteristics include focal length (the distance over which collimated light rays passing through the lens are brought to focus), optical center (the point of intersection of the optical axis at the image sensor), and lens distortion (radial and/or tangential distortion of an image captured using the lens). Consequently, for each of a virtually infinite number of lens positions available, ranging from a macro focus position to an infinity focus position, a corresponding set of intrinsic characteristics are typically applied to the captured image based on an accurate determination of the current location of the lens. Additionally, each of the intrinsic characteristics may be further influenced by the current temperature of imaging system. As a result, as the variable focus actuator moves the lens from one position to another, the position of the lens is typically determined (possibly along with the current temperature), and various intrinsic characteristics for the new lens position are applied. Those characteristics may have been previously stored for the new lens position, or may be interpolated based on stored intrinsic characteristics for one or more nearby lens positions.